Autodeposition, also known as autophoresis .RTM. or chemiphoresis, is a process for depositing an organic coating on a metal surface. The process involves the controlled release of multivalent metal ions from the metal surface which destabilizes dispersed polymer particles in the coating such that coating builds up on the metal surface. Such systems are well known in the coating art and are described in for example, U.S. Pat. Nos. 3,776,848, 3,791,431, 4,108,817, 3,839,097, 3,829,371 and 4,104,424.
Autodeposition, though a relatively new procedure for coating metal surfaces, has achieved considerable importance and wide use in the coating industry due to its many advantages over conventional systems, such as electrolytic deposition. By using autodeposition, practitioners of the art can now deposit an inorganic and an organic film simultaneously with fewer operating steps in less time while utilizing less floor space than conventional pretreatment/ electrocoating systems. Autodeposition also reduces the air and water pollution associated with conventional coating systems because organic solvent usage is minimized. The use of autodeposition also reduces significantly the energy usage required by certain conventional electrocoating systems. A further advantage is the sharply decreased safety risk attained by avoiding the use of electric current in the coating bath.
A major disadvantage of autodeposition coating is the inability to coat non-metallic surfaces with autodeposition coating systems since autodeposition requires some dissolution of the metal substrate to be coated to furnish metal ions to the autodeposition coating bath; furnishing of metal ions to the coating bath is essential to the autodeposition process. Thus it has heretofore been virtually impossible to autodeposit a coating onto such substrates as wood, ceramic, glass, plastic, etc. Further it has also heretofore been virtually impossible to autodeposit a coating onto any substrate, metallic or otherwise, on which there has been previously coated a non-metallic coating such as a polymeric coating.
This severe disadvantage has greatly hampered the utility of autodeposition systems and greatly restricted the uses and applications to which autodeposition could be put. Therefore, a method which would allow autodeposition onto a non-metallic surface would be of great utility and would be highly advantageous.